GB2116668A

GB2116668A - Thermally insulating hydraulic brake piston

Info

Publication number: GB2116668A
Application number: GB08306463A
Authority: GB
Inventors: Gino Villata
Original assignee: Valeo SE
Current assignee: Valeo SE
Priority date: 1982-03-12
Filing date: 1983-03-09
Publication date: 1983-09-28
Also published as: IT1171104B; ES520499A0; FR2523244A1; US4581985A; GB8306463D0; GB2116668B; FR2523244B1; IT8312455A0; BR8301184A; ES8401584A1; DE3308711A1

Description

1

SPECIFICATION

Hydraulically actuated brake incorporating a device to preventan excessive rise in the temperature of the 5 hydraulicfiuid This invention relates to a hydraulically actuated brake comprising at least one friction element, for example a brake pad in the case of a disc brake, adapted to be clamped against a rotating track by a piston fitted slidably in a cylindrical body in response to a build-up of pressure in an actuating chamber containing hydraulic fluid and defined in part by the said piston.

The invention relates particularlyto such a brake in 80 which the piston comprises a cup-shaped element having a cylindrical wall sliding in the cylinder and a base adjacentthe actuating chamber.

The cupforming the piston is usually madefrom metal for example, steel, and is applied directlytothe friction element. During braking, the heat generated bythefriction between thefriction element and the rotating track causes a rise in the temperature of the metal piston and consequently of the hydrauliefluid which is contained in the actuating chamber and in contactwith the base of the cup. There is a danger thatthe hydrauticfiuid, which generally consists of oil, may lose its operating efficiencywhen the temperature exceeds a given value, for example 15WC. It istherefore important that the heat generated byfriction should not causethe temperature of the hydrauliefluid to rise above such a value.

The invention relates particularlyto such a brake in which means are provided to prevent an excessive rise in temperature of the hydraluic f luid consisting of 100 a cylindrical core of mechanically strong and thermally insulating material fitted inside the cup forming the piston, the walls of the core and of the cup being fixed together by connecting means having a press fit.

The side walls of the core and of the cup are generally continuous, which permits a direct and effective press fit, but only under assembly conditions which necessitate high precision and which are in any case difficult because of the large su rface areas present. Moreover, the core frequently forms an insuff icient heat shield to prevent the temperature of the hydrau lic fluid from rising to an excessive value.

The object of the invention is a hydraulically actuated brake of the kind described above, in which the hydraulicfluid of the actuating chamber is protected in a particularly effective mannerfrom an excessive rise in temperature, and the assembly conditions for the pressfit of the core in the cup are improved.

According to the invention, a hydraulically actuated brake of the kind described above is characterised in thatthe press fit connecting means of the core in the cup are localised and involve only a part of the side walls of the core and of the cup, and provide an interstice between the remaining part of these side walls which mutually separates them.

By virtue of this arrangement, the air gap left by interstices between the cup and the core considerably improves the efficiency of the thermal insulation between the friction element which engages the UB 2 1 Ibbibb A 1 rotating track, and the cup-shaped piston which is in contact with the hydraulic fluid. Thus the hydraulic fluid is protectedfrom an excessive temperature rise and is not in dangerof losing its operational qualities.

Furthermore, duetothe above-stated localisation, engagement of thecore as a pressfit insidethe cup is made particularly easy, both whenthe pressfit connecting meansconsistof the actual sidewalls of the core and of the cup, and also when they consist of one or more separately-inserted elements interposed between these side walls.

According to a feature of the invention, the press fit connecting means consist of localised regions of the actual side walls of the core and of the cup.

These localised regions are formed by protuberances of the core or of the cup and are engaged with the regular surface of the other element, or preferably in recesses made in this other element.

The localised regions are at least partly linear and extend, for example, along generatrices of the cup, particularly over a part of the height of the cup preferably close to its base. These localised linear regions may likewise be annular or. generallyspeaking, have any appropriate arrangement. The localised regions may likewise be at least partly punctual.

As a variant,the localised regions consistof a projecting helicoidal thread made in the side wall of the cup and slightly embedded in the sidewall of the core. In this casethe pressfit engagement is performed not by an axial action but by a screwing action.

According to anotherfeature of the invention the press fit connecting means of the core in the cup consist of one or more separate elements interposed between the side walls of the core and of the cup.

These interposed elements may be engaged directly between the ordinary surfaces of the core and of the cup, or in recesses of the core andlor of the cup.

In one embodiment, the interposed elements comprise lugs extending along generatrices and equipped with hooking noses. Such lugs may be separate orjoined together into a single piece by a stellate base placed on the base of the cup.

In anothervariant, the construction of which is particularly simple and effective, the interposed element consists of a slit, externally toothed elastic washer engaged in an annular groove of the core, this groove exhibiting a tapered flankto givethe washer, upon the engagement of the core in the cup, an inclination which permits such an engagement but which, when once the core has reached the base of the cup, fixesthese two pieces together by buttress effect of the booth system of the washer againstthe cup.

Preferably, whateverthe form of the connecting means between the core and cup, the core overlaps the cup so the external face by which the piston is made to engagethe friction element is defined bythe core of the exclusion of the cup.

In an embodiment, the core is of friction lining material containing fibres, fillers and a binder.

In orderthatthe invention may be more fully understood, embodiments in accordance therewith will now be described by way of example with reference to the accompanying drawings, in which:

2 GB 2 116 668 A 2 Figure 1 is a general schematic view in section of a brake according tothe invention,the piston of which comprises a cup receiving a core of mechanically strong and thermally insulating material; Figure 2 is a viewof this piston in cross-section along the line 11-11 of Figure 1; Figure 3 is a view in side elevation of the core; Figure 4 is an end view of this core according to the arrow WAV of Figure 3; Figure 5 is a view in perspective of the core; 75 Figure 6 is a similarviewto Figure 2, but relates to a variant in which the protuberances of the core are engaged in recesses of the cup; Figure 7 is a similarviewto Figure 6, but relatesto anothervariant in which the protuberances are provided on the cup and are engaged in recesses of the core; Figure 8 relates to another variant in which the protuberances of the core are annular; Figure 9 relatesto anothervariant in which the protuberances of the core are punctual; Figure 10 relatesto another variant in which the core is slightly embedded by screw engagement in a projecting helicoidal thread of the sidewall of the cup; Figure 11 is a similarviewto Figure 6 or Figure 7, but relatesto anothervariant in which shims are inserted between the core and thecup and are engaged in recesses of the core and of the cup; Figure 12 relates to anothervariant in which an interposed element in the form of a tripod is disposed between the core and the cup; Figure 13 showsthis tripod in perspective; Figure 14 is a similarviewto Figure 13, but in which the tripod is replaced bythree distinct lugs; Figure 15 relates to yet anothervariant, in which an interposed element in the form of a slit, toothed elastic washer is inserted between the core and the cup; Figure 16 shows this washer in elevation; 105 Figure 17 is a similarviewto Figure 15 but during the assembly of the core in the cup.

Reference is made atfirstto Figures 1 to 5which relate, byway of a non-limiting example,to the application of the invention to a hydraulically actuated disc brake, particularlyfor a motorvehicle.

Figure 1 shows, at 10, the brake disc which has two opposite friction tracks 11 A and 11 B adapted to frictionally engage two friction elements comprising brake pads 12A and 12B. Each pad 12A, 12B consists of a friction lining material 13 fixed to a support 14. Each pad 12A, 12B is adapted to engage the corresponding friction track 1 1A, 11 B of the disc 10 by the free surface 15 of the lining 13 which is opposite the support 14. It isthus the support 14which transmitsthe force to each pad 12A, 12B to clamp it againstthe disc 10.

The brake comprises a caliper 16which is disposed overthe disc 10 and in which the brake pads 12A and 12B arefitted. The caliper 16 formsthe body of a cylinder 17 in which a piston, generally designated 18, is slidably fitted.

The piston 18 comprises an outerface 19 by which it is madeto engage the supprt 14 of the strip 12A. The piston 18 defines, in the cylinder 17, an actuating chamber 20 which is filled with hydraulic fluid,for example oil. Pressurised hydraulic fluid can be admitted to the chamber 20through a channel, shown at 21, which communicates with the chamber 20.

The caliper 16 likewise comprises a reaction face 22 againstwhich the support 14of the other brake pad 12B comes to bear.

The pads 12A and 12B are thus adapted to be clamped againstthe rotating tracks 1 1A and 11 B of the disc 10 bythe action of the piston 18 sliding in the cylinder 17, in response to a build-up of pressure in the actuating chamber 20.

The piston 18 (Figures 1 to 5) comprises a cup-shaped elementor hollow body 23 having a cylindrical sidewall 24 engaged withinthe cylinder 17 and a base 25 adjacentthe actuating chamber20. In the example shown in Figure 1,the cup 23 is castfrom steel. The piston 18 also comprises a cylindrical core 26 of thermally insulating and mechanically strong material. The core 26 is housed in the cup 23 and extends beyond the latter. The outerface 19, by which the piston 18 engagesthe pad 12A, is thus defined by the insulating core 26 and notthe cup 23.

The thermally insulating and mechanically strong material of which the core 26 is made is a brake friction lining material containing fibres, fillers and a binder. This material may contain, for example, a percentage byweight of 30% glass orasbestos fibres, 50% mineral filler such as calcium carbonate, and 20% of a bindersuch as phenolic resin.

The sidewalls of the core 26 and of the cup 23 are mutually engaged by pressfit connecting means L which are localised and which involve only a part of the sidewalls of the core 26 and of the cup 23Jorming in the remaining part of these sidewalls an interstice M filled with airwhich mutually separates them.

In the example shown in Figures 1 to 5, the pressfit connecting means L consist of localised regions Z of the actual sidewalls of the core 26 and of the cup 23.

These localised regions Z areformed by protuberances 27 on the core 26. Particularly, the localised zones Z are at least partly linear. The localised linear zones Zformed bythe protuberances 27 extend along generatrices of the cup 23 over a part of the height of the side wall 24 of the cup 23 which is nearthe base 25 of the cup 23. The lowerface of the core 26 likewise has protuberances 28 which are linear and radial.

Itwill be appreciated thatthe conditions of assem- bly of the core 26 in the cup 23 by a press fit are particularly easy since the side surface contact between the core 26 and the cup 23 is divided into the localised regions Z.

The localised regions Z likewise have the effect of improving the thermal insulation between thefriction elements 12A and the f luid in the hydraulic chamber 20.

During braking a pressure is admitted through the pipe 21 into the actuating chamber 20, which pushes the piston 18 against the pad 12A and produces clamping of the disc 10 between the pads 12A and 1213. The heat developed by this frictional engagement is transmitted only minimally to the base 25 of the cu p 23, by vi rtue of the insulating core 26 which forms a heat shield; the efficiency of this shield is 11 3 GB 2 116 668 A 3 improved duetothe air gapssuch as M which are formed in the cup 23 bythe core 26 between the protuberances 27 and 28. Thusthe hydraulicfluid in thechamber20 is protected from an excessive rise in temperature,which mightcause itto lose its qualities and its operational efficiency.

As a variant (Figure 6) the arrangement is similarto that wh ich has just been described with reference to Figures 1 to 5, but the protuberances 27 on the core 26 are engaged in recesses 29 in the cup 23. Thus the conditions of press fit engagement of the core 26 in the cup 23 are made still more precise and easy.

In anothervariant (Figure 7) the localised regions Z are formed by protuberances 30 on the cup 23. These protuberances 30 are advantageously engaged in recesses 31 in the core 26.

In anothervariant (Figure 8) the localised linear regions Z are formed respectively by annularflanges 32 on the core 26 coaxial with the piston 18, and the lower face of the core comprises an annularflange 33. 85 In another variant (Figure 9) the localised regions Z are at least partly punctual and formed particularly by projecting studs 34, and the lowerface of the core likewise comprises projecting studs 35.

In anothervariant (Figure 10) the localised regions Z consist of a projecting helicoidal thread 36 formed in the side wall of the cup 23 and slightly embedded in the side wall of the core 26. In this case the press f it engagement is effected by a screwing action. The air gap M is disposed between the turns of the thread 36.

In the embodiments so far described, the connecting means L consist of localised regions Z of the actual walls of the core 26 and of the cup 23.

Inthe embodiments which will now be described, the connecting means L consist of one or more separate elements C interposed between the core 26 andthecup23.

Referring to Figure 1 1,the arrangement here is similartothat of Figure 6 orthat of Figure 7, and the elements C consist of shims 37 arranged along generatrices and inserted between the core 26 and the cup 23. These shims 37 are advantageously engaged in recesses 38 in the cup 23 andlor in recesses 39 of the core 26.

In another variant (Figures 12 and 13) and elements 110 C comprise lugs 40 which extend along generatrices and which are equipped with hooking noses 41.

These lugs 40 are joined by a stellate base 42 to form a single, generally tripod-shaped piece.

In the assembly position of Figure 12, the lugs 40 are inserted between the side walls of the core 26 and of the cup 23 with a hooking effect by noses 41, and the base 42 is inserted between the lower wall of the core 26 and the base of the cup 23. As previously, air gaps arethen formed between the lugs 40.

The assembly is per-formed easily by a pressfit effect.

In anothervariant (Figure 14) the arrangement is similarto thatwhich hasjust been described with referenceto Figures 12 and 13, butthe lugs 40 are formed by seperate pieces. - In another variant (Figures 15 to 17), the construction of which is particularly simple and effective, the element C consists of an elastic washer 50 slit at 51 and externally toothed 52 (Figure 16). The washer 50 is adapted to be engaged in an annular groove 53 in the core 26.

The groove 53 isformed with a tapered flank 54 in orderto give the washer 50, when the core 26 is engaged (Figure 17) in the cup 23, an inclination (Figure 16) which permits engagement butwhich, when once the core 26 has reached the base of the cup 23Joins these two pieces together by a jamming effect of the toothed washer 50 against the cup 23. As

Claims

previously, an air gap M isformed between the side walls of the core 26 and of the cup 23. CLAIMS

1. A hydraulically actuated brake, comprising at least one friction element adapted to be clamped against a rotatable friction track by a piston fitted slidably in a cylinder body in response to an increase in pressure in an actuating chamber containing hydraulic fluid and defined in part by said piston, wherein the piston comprises a cup-shaped member having a cylindrical side wall engaged within the cylinder, and abase adjacent said actuating chamber, and a cylindrical core of mechanically strong and thermally insulating material engaged within the cup-shaped member, the side walls of said core and of said cup being fixed together by press-fit connecting means, and wherein said connecting means are localised and involve only a part of the side walls of said core and said cup, forming between the remaining part of these side walls an interstice which mutually separates them.

2. A brake according to Claim 1, wherein the press-fit connecting means comprise localised regions of the actual side walls of the core and of the cu p.

3. A brake according to Claim 2, wherein said localised regions are formed by protuberances on the core.

4. A brake according to Claim 3, wherein the protuberances on the core are engaged in recesses in thecup.

5. A brake according to Claim 2, wherein said localised regions are formed by protuberances on the cu p.

6. A brake according to Claim 5, wherein the protuberances on the cup are engaged in recesses in the core.

7. A brake according to anyone of Claims 2to 6, wherein said localised regions are at least partly linear.

8. A brake according to Claim 7, wherein said localised linear regions extend along generatrices of the cup.

9. A brake according to Claim 8, wherein said localised regions along the generatrices of the cup extend over part of the height of the side wall of the cup.

10. A brake according to Claim 9, wherein said partof the heightof thesidewall of the cup is closeto the base thereof.

11. A brake according to Claim 7, wherein said localised linear regions are annular and coaxial with the piston.

12. A brake according to Claim 2, wherein the localised regions consist of a projecting helicoidal thread formed inthe side wall of the cup and slightly 4 GB 2 116 668 A 4 embedded in the side wall of the core.

13. A brake according to Claim 1, wherein said press-fit connecting means comprise separate means interposed between the side walls of the core and of the cup.

14. A brake according to Claim 13, wherein said separate means comprise shims engaged in recesses in the cup.

15. A brake according to Claim 13 or 14, wherein said seprate means comprise shims engaged in recesses in the core.

16. A brake according to Claim 13, wherein said means comprise lugs extending along generatrices and equipped with hooking noses.

17. A brake according to Claim 16, wherein said lugs are joined into a single piece by a stellate base.

18. A brake according to Claim 13, wherein said means comprise a slit and toothed elastic washer engaged in a groove in the core.

19. A brake according to Claim 18, wherein said groove has a tapered flank so as to incline the washer during the engagement of the core in the cup.

20. Abrake accordingto anyone of Claims 1 to 19, wherein the core extends beyond the cup so that the outerface by which the piston engages the friction element is provided by the core and not the cup.

21. Abrakeaccording to anyone of claims 1 to 20, wherein the core is made of a friction lining material containging fibres, fillers and a binder.

22. A hydraulically actuated brake, substantially as hereinbefore described with reference to Figures 1 to 5, Figure 6, Figure7, Figure 8, Figure 9, Figure 10, Figure 11, Figures 12 and 13, Figure 14, or Figures 15 to 17 of the accompanying drawings.

Printedfor Her Majesty's Stationery Office by The Tweeddale Press Ltd., Berwick-upon-Tweed, 1983. Published atthe PatentOffice, 25 Southampton Buildings. London, WC2A lAY, frornwhich copiesmay be obtained.